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kimbomba

Fri Apr 29 2011, 03:53AM

Registered Member #3854 Joined: Fri Apr 29 2011, 03:45AM
Location: Mexico
Posts: 95

Hi everybody i am new to the forum and also new to HV, but i have already built a coil gun, a single transistor flyback driver and a boost converter cap charger. Today i bought my first NST, an Allanson 15 KV 30 ma unit. Sorry if the question has been answered but I searched the forum with no success. What are the general recommendations for taking care of a NST. Particularly I would like to know if I can run the transformer with a variac; i have seen videos where this is done but, Â¿it is safe for long time periods? Thanks in advance

ScotchTapeLord

Fri Apr 29 2011, 04:11AM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

If you are using the variac to lower the voltage then that will stress the transformer less than regular operation.
If you are using the variac to raise the voltage beyond line level then that could cause harm.

It seems that model of transformer may have ground fault protection. That will prevent arc-drawing.

James

Fri Apr 29 2011, 05:22AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Generally speaking, there should be plenty of overhead to safely run the input at 140V, the max most variacs go to. As was already said, going lower than rated is no problem.

I've never actually worked with one of the ground fault protected transformers. Can't the protection be bypassed?

Xray

Fri Apr 29 2011, 01:56PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

I've played with NST's over the years, and the best thing about them is the fact that they are intrinsically current-limited. What that means is, you can short-circuit the secondary winding, and it will never source more than it's rated current (30mA in your case). BUT (and this may be important) the NST may not be able to limit the secondary current if operated below its rated input voltage (I say "may" because I'm not certain). If operated at a lower voltage, the core may not saturate, which would allow the secondary to source current beyond its nominal value.

Comments?

Adam Munich

Fri Apr 29 2011, 02:16PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

An NST doesn't limit current via saturation, instead it has magnetic shunts between the windings to increase leakage inductance. I don't think any transformers are designed to be run at saturation.

Proud Mary

Fri Apr 29 2011, 02:45PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Grenadier wrote ...

I don't think any transformers are designed to be run at saturation.

Saturable transformers are used in some specialist applications, e.g.

Rev. Sci. Instrum. 63, 2138 (1992); doi:10.1063/1.1143180 (3 pages)
Magnetic pulse compressor using saturable transformer to excite excimer lasers
K. Kurihara, S. Kobayashi, I. Satoh, K. Shibata, M. Shigeta, K. Masugata, and K. Yatsui

To reduce the load on switching elements in the excitation circuit of excimer lasers, a new circuit has been developed to study the basic characteristics, where a saturable transformer is utilized in the magnetic pulse compressor. We have used a saturable transformer with a winding ratio of 1:4. The initial pulse of 8.5 kV, 2.0 kA, 3 Î¼s was transferred to the output pulse of 34 kV, 8 kA, 109 ns, with an energyâ€transfer efficiency of 58%. Using a saturable inductor as a charging inductor, furthermore, we have succeeded in reduction of the prepulse of the output voltage and enhancemet of the energyâ€transfer efficiency

Xray

Fri Apr 29 2011, 03:33PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Grenadier wrote ...

An NST doesn't limit current via saturation, instead it has magnetic shunts between the windings to increase leakage inductance. I don't think any transformers are designed to be run at saturation.

There are "saturable reactors", but you are correct about the NST not saturating. (my bad). It limits current by shunting some of the magnetic flux away from the secondary winding, causing (as you said) leakage inductance.

Adam Munich

Fri Apr 29 2011, 04:20PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Where do you find all these random documents proud mary?

Proud Mary

Fri Apr 29 2011, 05:44PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Grenadier wrote ...

Where do you find all these random documents proud mary?

Not random is the answer.

Condense the arg into a few words or phrases which are only likely to occur together in a document containing information of the desired sort.

You must first define what you are looking for in order to find it.

James

Fri Apr 29 2011, 05:50PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I recall the old Sola voltage regulating transformers used saturation to regulate the line voltage. They used to be common for computer equipment although you don't see them much anymore. I remember they ran hot and often were a bit noisy.

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